Few studies have examined sexual risk behaviors among heterosexual methamphetamine (MA) users. MA has become the leading drug of abuse among young people in Thailand over the past decade. MA has been associated with increased sexual risk behavior in many contexts, and relatively little is known about its impact in this population. Existing research shows high levels of sexual risk among Thai young people, but data are limited regarding individual and social influences on sexual behavior. Despite decades of HIV prevention in Thailand, HIV prevalence remains high, particularly in certain population segments. There is great concern about HIV transmission potential among young Thai MA users as HIV enters their social networks. The proposed study will explore individual and social dimensions of sexual risk behavior in a cross-sectional sample of 18-29 year old current MA users and members of their drug and sexual networks in Chiang Mai Province, Thailand. The specific aims are to: 1) qualitatively explore the social context of sexual behavior among Thai MA users; 2) examine the association between individual-level factors, such as demographic characteristics, drug use patterns, depression, and STI history, on sexual risk behavior; 3) examine the association between social-level factors, such as network characteristics, relationship characteristics, social support and social norms regarding sexual behavior on sexual risk behavior; and 4) model the relationship between and among individual, relationship, and social network factors in predicting sexual risk behavior. In-depth interviews and qualitative analysis methods will be used to address Aim 1; bivariate and multivariate statistical analyses will be used to address Aims 1-3. Findings will inform HIV prevention efforts addressing social as well as individual influences on behavior. [unreadable] [unreadable] [unreadable]